Congratulations on deciding to join our glorious pc gaming master race :thumbsup: All your troubles are over.
You may want to wait a month or two until the problems with the new intel sandy bridge motherboards are fixed and until AMD's new bulldozer cpu is released. However if you must build now then this would do:
CPU - Athlon II x4 £80 - good basic quad core
http://www.overclockers.co.uk/showpr...d=6&subcat=803
Graphics card - GTX 560ti £198 - most important part for gaming, this is an excellent value very strong gaming card, will run pretty much anything out there
http://www.overclockers.co.uk/showpr...14&subcat=1341
RAM - 4GB DDR3 £35 - all you will need for now
http://www.overclockers.co.uk/showpr...=8&subcat=1517
PSU - Corsair 650w £71 - probably a bit overkill but its a good quality PSU, never skimp on the PSU
http://www.overclockers.co.uk/showpr...id=123&subcat=
Motherboard - GA-870A-UD3 £82 - dont need anything more than a basic mobo
http://www.overclockers.co.uk/showpr...03&subcat=1782
Case - Antec 300 £53 - very good case, easy to work with, strong steel not plasticky at all
http://www.overclockers.co.uk/showpr...d=7&subcat=160
Total = £484
There ya go, should run most things and theres extra money for you to pick a monitor/keyboard/mouse of your choice if you need those things. Plus thats all from overclockers.co.uk you can sometimes find the same things cheaper on ebuyer.com or dabs, overclockers only really makes sense if they have a special deal and you have the free delivery for being a loyal forumer. Also dont forget a DVD drive, any will do theyre all good enough.